A conventional dispensing system for supplying heated adhesive (i.e., a hot-melt adhesive dispensing system) generally includes a melter having an inlet for receiving adhesive materials in solid or semi-solid form, a heater grid in communication with the inlet for heating and/or melting the adhesive materials, and an outlet in communication with the heater grid for receiving the heated adhesive from the heated grid. The outlet communicates with a pump for driving and controlling the dispensation of the heated adhesive through the outlet and to downstream equipment, such as dispensing modules. Furthermore, conventional dispensing systems generally include a controller (e.g., a processor and a memory) and input controls electrically connected to the controller to provide a user interface with the dispensing system. The controller is in communication with one or more of the melter, the pump, and other components, such that the controller controls the dispensation of the heated adhesive.
Conventional hot-melt adhesive dispensing systems typically operate at ranges of temperatures sufficient to melt the received adhesive and heat the adhesive to an elevated application temperature prior to dispensing the heated adhesive. In order to ensure that the demand for heated adhesive from the gun(s) and module(s) is satisfied, the adhesive dispensing systems are designed with the capability to generate a predetermined maximum flow of molten adhesive. For example, the inlet of the melter communicates with a fill system operated by the controller of the dispensing system. In a typical arrangement, the fill system operates to deliver a stream of solid particulate or pelletized adhesive using a pressurized air flow from a bulk supply or source of the solid adhesive to the inlet of the melter whenever a receiving space (e.g., hopper) above the heater grid requires refilling. In these arrangements, the melter also includes an exhaust outlet with a filter for discharging the pressurized air flow from the fill system or receiving space after that pressurized air flow has delivered the solid adhesive into the receiving space. Thus, each fill system cycle requires the exhausting of pressurized air flow out of the melter.
As readily understood, the exhaust air filter will become clogged over time as the fill system is used. This clogging of the exhaust air filter stifles the efficient operation of the fill system because it can limit the amount of pressurized air flow generated through the fill system and the melter. Conventional adhesive melters and dispensing systems do not specifically monitor the use of the exhaust air filter, so there is currently no known mechanism in this field to provide predictive maintenance information to an operator regarding when the exhaust air filter will need to be replaced. Instead, conventional systems typically continue to operate until the exhaust air filter is so clogged that the fill system effectively cannot keep up with the demands for molten adhesive from the melter, such as when the dispensing system requires the predetermined maximum flow of molten adhesive. Alternatively, the fill system may also stop working for other reasons such as a burst hose in the fill system or an obstruction of flow at the source of adhesive. As a result, a shutdown of the fill system occurs, which can eventually lead to the melter running out of adhesive and shutting down as well. Therefore, the adhesive dispensing system undergoes a period of unplanned downtime until maintenance personnel can identify the issue with the clogged exhaust air filter (or the other issues described above, when applicable) and then perform appropriate maintenance, such as a replacement of the exhaust air filter. These unplanned downtimes for the system are undesirable and costly for operators of conventional adhesive melters and dispensing systems.
In other pneumatic fields such as HVAC systems, air filters have been monitored using air flow measurement devices and/or pressure detection sensors that provide estimates of how much air flow moves through the air filter. The air filters in these other fields are then replaced after a set amount of air flow has passed through the air filter. While this type of equipment could hypothetically be used in the conventional adhesive melters, this equipment has not been added for multiple reasons. First, the additional air flow measurement devices and/or pressure detection sensors add additional cost to the manufacturing and maintenance of the adhesive melter, and this additional cost may outweigh the benefit of attempting to provide predictive maintenance information about the exhaust air filter at the adhesive melter. Second, these types of predictive maintenance based on total air flow through the exhaust air filter are unreliable in this context because exhaust air filters in adhesive melters are subject to highly variable conditions that may significantly alter the lifespan or total air flow that the exhaust air filter can pass through before clogging. Thus, merely measuring the total air flow through an exhaust air filter at an adhesive melter is not a reliable method for accurately determining when the exhaust air filter will become clogged, and unplanned downtimes for the adhesive melter would likely still occur.
The highly variable conditions that subject the exhaust air filters to unpredictable lifespan include the use of different adhesive materials or variable pellet shapes/form factors with filters, as these different materials or form factors can affect the amount of air flow required to move the solid adhesive. In another example, the length of hose used between the source of adhesive for the fill system and the melter may also affect the cycle time for a fill system and the lifespan of an exhaust air filter. In some instances, a more significant source of unpredictability in the lifespan of exhaust air filters is the selective use of powder that may be put on the solid adhesive to prevent tackiness and sticking together of the pellets or particles before delivery to the receiving space. This powder causes more rapid clogging of the exhaust air filter at the melter, thereby shortening the lifespan of the exhaust air filter. Furthermore, the use of powder on certain batches of solid adhesive delivered to the bulk supply from which the fill system draws solid adhesive is unpredictable because not every batch of solid adhesive may include the powder (e.g., the powder may only be used at hotter times of the year when the adhesive supplier and the ambient conditions at the bulk supply may be more prone to pellets sticking together). The amount of powder on the adhesive that will be captured by the exhaust air filter may also vary dramatically even between different batches or fill system cycles. As a result, it is currently impractical to reliably predict when an exhaust air filter in a conventional adhesive melter will require replacement. Furthermore, there is currently no known method for distinguishing reduced performance of the fill system caused by exhaust air filter clogging from reduced performance of the fill system caused by other problems such as burst hoses or adhesive supply obstructions.
For reasons such as these, an improved adhesive melter and method of operation, including a control process for accurately predicting and alerting an operator when an exhaust air filter requires replacement or maintenance, would be desirable.